1. Field of the Invention
This invention relates generally to a solid-state laser device. More particularly, the present invention relates to a semiconductor laser device of the type which utilizes a semiconductor laser chip hermetically encased in a cap.
2. Description of the Prior Art
Various semiconductor laser devices have been heretofore proposed. One typical example of these is the one which incorporates a semiconductor laser chip hermetically encased in a cap. The cap serves to protect the laser chip against adverse influences which may be caused by environmental moisture and/or dust. The cap also protects the laser chip against shocks and/or contact with external objects.
The capped semiconductor laser device is disclosed for example in U.S. Pat. No. 4,768,070 (Patented: Aug. 30, 1988; Applicant: Takizawa et al) or in Japanese Utility Model Application Laid-open No. 62-58066 (Laid-open: Apr. 10, 1987; Inventor: Toshiyiko Ishii). Reference is now made to FIGS. 31 through 33 of the accompanying drawings to specifically describe the prior art arrangement of such a laser device.
As shown in FIGS. 31 through 33, the typical prior art semiconductor laser device includes a discal base or stem 1 of a suitable diameter D and thickness T. The stem is provided with an upwardly directed mounting block 2 for mounting a semiconductor laser chip 3 via a semiconductor substrate (submount) 4. The discal stem is made of a metal such as carbon steel, and works dually as a support and as a heat sink.
The stem 1 is formed, near the mounting block 2, with an inclined recess 9a for arranging a laser emission monitoring photodiode 9. The underside of the stem is welded to a first lead 7a in electrical conduction therewith. Further, the stem is formed with a pair of lead inserting holes 1a, 1b to allow insertion of second and third leads 7b, 7c. The second and third leads are hermetically insulated from the stem by insulating glass sealant 8 loaded into the respective lead inserting holes.
As shown in FIG. 32, the laser chip 3 is connected to the substrate 4 by a wire A, while the substrate 4 is connected to the second lead 7b by another wire B. Similarly, the third lead 7c is connected to the photodiode 9 by a further wire C.
The laser device further comprises a cap 5 having a glass window plate 6 and mounted to the stem 1 to encase the semiconductor laser chip 3 and its associated components. The cap is also made of a metal such as carbon steel, and hermetically attached to the stem 1 by performing resistance welding. The glass window plate 6 is hermetically attached to the cap by using glass solder.
In operation, when a predetermined current is passed, the semiconductor laser chip 3 generates a laser beam in the arrow direction (FIG. 11) by stimulated emission. Simultaneously, a portion of the laser beam is emitted in the opposite direction and detected by the photodiode 9 for monitoring the laser beam emission.
The prior art laser device described above has the following technical problems.